In testing with server 2016 - the only thing I ran into was firewall ports so far. I was also pushed to upgrade to MS SQL 2016 as well.
We Are looking to do a full system test against Windows 2016. So far I have not seen any issues with testing 6.1 SP3 on it. SQL 2016 has not generated any issues either so far.
If you do see any quirks please open a ticket with support and we can look to fix it.
We will provide an updated systems specification matrix with the release of Avalanche 6.2